AFAIK, the only way to adjust the front preload is to change out the springs. AZTOM here has done that on his R², so he might chime in on that.. but you might have to ask him in the general forum. From what i understand, the x front springs are optomized for about a 200# rider.. a little stiff for me, but i've just lived with it. Maybe someday i'll swap out the front springs, or trade with someone who wants the stiffer x springs. The back is the same, which is why many get the 'pogo' effect. We try to take out some of the stiffness of the springs by turning the compression & rebound damping way down, but then the stiff spring just launches you over the bars.
I guess yamaha wanted to make it as universal as possible, & still have some handling for 2 up riders. I suppose a suspension makeover is necessary to really dial it in for each of our riding styles & unique characteristics.